1
# Definition for singly-linked list.
2
# class ListNode:
3
#     def __init__(self, val=0, next=None):
4
#         self.val = val
5
#         self.next = next
6
class Solution:
7
    def deleteDuplicates(self, head: Optional[ListNode]) -> Optional[ListNode]:
8
        if head is None:
9
            return head
10
        cur = head.next
11
        prev = head
12
        while cur is not None:
13
            if cur.val == prev.val:
14
                prev.next = cur.next
15
            else:
16
                prev = cur
17
            cur = cur.next
18
        return head